1. Field of the Invention
The invention relates, generally, to the touch interfaces and the control of an equipment item or of a function by means of such an interface. A particularly advantageous application of the invention relates to the control of equipment items or functions embedded onboard an aircraft and in particular in the field of avionics.
2. Description of the Relevant Art
Currently, the cockpit of an airplane is provided with a set of instruments and interfaces necessary to the piloting of the aircraft. These instruments and interfaces combine a set of buttons and actuators, with one or more states that make it possible, when actuated, to operate an avionics equipment item or function.
As is understood, some avionics equipment items or functions are likely to involve systems qualified as “critical” in as much as the change of state of the buttons or actuators that control them can have a direct impact on the flight. Activating them at the wrong moment can thus provoke incidents that might possibly end in a disaster.
Several scenarios can lead to such incidents.
They can firstly result from an erroneous activation, when the pilot presses the wrong button.
They can also be activated accidentally, when the pilot engages a button without noticing, for example when a clothing item becomes caught on a button or a lever or when an object drops onto it.
Of course, currently, various means are implemented to limit these wrong activations.
They can firstly involve organizing specific procedures requiring the pilots to sequence their action in a predefined and secure order or requesting the acknowledgement of an act by the user him or herself or by another user.
They can secondly involve modifying the arrangement of the buttons or levers so as to avoid inopportune manipulations.
With this in mind, it is known practice to provide for a mechanical interlocking of the buttons so that the pilot has to perform the activation with both hands or by two gestures, thus limiting careless mistakes.
It is also known practice to design buttons that have different shapes so that the pilot becomes accustomed to a touch associated with these functions. For example, one button can have a shape or a direction of activation that differs from the others.
Provision can also be made to produce the buttons using different materials or colors, a bright color potentially requiring particular attention from the pilot.
It is also possible to provide for the button or a lever to be physically protected against inadvertent activations. For example, a button can be placed in a recess, a wall or a shutter potentially provided to prevent an object or a clothing item catching on and activating the button.
Having the buttons and levers positioned in areas that are moderately accessible or that require a particular effort on the part of the pilot also makes it possible to avoid inopportune manipulations by ensuring that the pilot, when he or she has contacted the interface concerned, has done so intentionally.
It is, moreover, known practice to provide for functions or equipment items to be disabled by software in cases where there is no reason for them to be activated.
Moreover, the current trend is to dematerialize the human-machine interfaces conventionally based on the use of control buttons or levers and to implement them by means of touch interfaces using LCD screens on which graphical objects are displayed that simulate the functions or equipment items to be controlled.
As will be understood, the transition from a hardware control member to a touch button on the LCD screen renders some of the protections used conventionally to avoid wrong activations obsolete, in particular those linked to the use of locks, shutters, or, generally, protection elements preventing mechanical operation of control members before preliminary action on the protection elements.
Thus, with the advent of human-machine touch interfaces, there emerges the problem of how to secure critical functions, which becomes more acute in the aeronautical field.
It will also be understood that, while touch screens do indeed offer enhanced ease of use, their use deprives the user of a spatial dimension of use. Such is in particular the case with a function which, when it can be activated by means of a pushbutton, requires a positive action on the part of the user tending to depress the button whereas simply brushing a graphical object on an LCD screen makes it possible to activate this function such that the first level of security of this function disappears with the transition to a touch interface.